Interference eliminating means for radio receiving circuits



NOV. 26, 1940. BOLE 2,222,739

INTERFERENCE ELIMINATING MEANS FOR RADIO RECEIVING CIRCUITS Filed Jan. 17, 1939 "OWL/NE .5. i i ie Patented Nov. 26, 1940 UNITED STATES PATENT OFFICE INTERFERENCE ELIMINATING MEANS FOR RADIO RECEIVING CIRCUITS Application January 17, 1939, Serial No. 251,417

3 Claims.

This invention relates to the elimination of interference in radio receiving circuits. In my co-pending United States patent application Serial No. 240,895, I have disclosed a means of 5 eliminating power line interference in radio receiving circuits. This means is variable by the provision of a series of switches whereby power line interference arising from various different sources may be eliminated at the same time.

According to the present invention the same principle is employed and a similar type of unit is used in conjunction with the power line connections. I have found, however, that by employing this unit together with an additional unit in the antenna connecting lead, so combined as to co-operate one with the other, that, not only do I reduce power line interferences as well as interference arising through the antenna of the receiving set, but the combination apparently has an interrelated effect such that interference from both sources appears to be materially reduced to a greater extent than would be the case in eachinstance where these devices were employed independently of one another.

It is, therefore, an object of the present invention to provide means for eliminating radio interference both from the power line and the antenna lead which may be varied according to conditions obtaining to reduce interferences from all sources to a minimum.

A further object of the invention is to provide a device of this character which maybe built in a simple unit to include simple means for varying the effect of the device to reduce the interference and by means of such variation to meet the interference characteristics existing in different calities.

A still further object of the invention is to provide a development embodying means for eliminating power line interference as wellas means for eliminating antenna interference wherein either of these two may be set up independently to achieve good results in reducing interference in their respective fields.

With these and other objects in view, the invention comprises the use of an inductance coil in series with the antenna inductively coupled with a pair of inductance coils suitably connected between the two sides of the power line and ground, condensers of suitable size being included in series with the leads connecting the said coils with the power lines. By these means currents at interfering frequencies arising in the antenna may be cancelled out by the action of currents at the same frequencies which are set up simultaneously in the power line.

The invention will be understood by reference to the following detailed specification taken in conjunction with the accompanying drawing.

In the drawing,

Figure 1 is a general wiring diagram of the interference eliminating means shown in the form of a co-operating combination of elements set up between a power 'line and the antenna of radio receiving apparatus.

Figure 2 is a detail elevation of one manner in which the series of inductively coupled inductance coils may be set up wherein two of the coils may be adjusted, and

Referring to the drawing Ill indicates the leadin from the antenna of radio receiving apparatus and including the inductance coil II in series at any suitable point between the antenna and the connection [2 with the receiving apparatus. Numerals l3 and I4 indicate the power line to which is connected the interference eliminating unit, embodying a combination of inductances, condensers, resistances and ground, as fully described in my co-pending application above referred to and which will be described in more detail hereunder.

In addition to this power line interference reducing means there is included two lines 15 and I6 connected with the power line preferably via the leads I! and I8 and commonly connected with ground as indicated at [1. The lines I5 and I6 incorporate inductance coils I9 and 20 designed to be inductively coupled with the inductance coil II and so arranged that the coupling between these coils and the antenna coil may be variable. When this coupling is properly adjusted the effect of any interfering frequency arising simultaneously in the antenna and in the power line will be cancelled out due to the reaction of the electromagnetic fields produced by the interfering current in coil II and the currents of similar frequency flowing in coils l8 and 20.

One wayof providing for variations of the inductances l9 and 20 is illustrated in Figure 2, wherein the three coils ll, l9 and 20 are mounted upon a common base B, the coils l9 and 20 being pivotally carried on each side of the coil ll so that by swinging these coils towards or away from coil H the desired variations may be obtained.

The means for eliminating power line interferences embodies the inductance coils 2| and 2 la connected across the power line by way of the leads 22 and 23 respectively which incorporate resistances and condensers 22a, 22b and 23a and 23b, respectively, as Well as an appropriate switch 220 and 230 respectively in each line. Each line 5 is also connected via the leads 24 and 25 by way of appropriate switches 2 5a and 25a to ground as at 26, including the condenser 21 selectively connected into the circuit, if required, by operating switches 26a and 26?) as referred to in my 10 previous application.

It will be appreciated that the coils l9 and 20 connected across the power line and inductively coupled with the coil ll of the antenna may be used effectively as a unit alone for reducing interference transmitted through the antenna. However, by using these devices in combination, namely, the power line interference reducing unit embodying coils I9 and 2d inductively coupled with coil ll of the antenna, I obtain an added improved effect which -I believe results from the fact that by utilizing the power line interference reducing unit, to by-pass a large proportion of energy at the interfering frequency arising through the power line, as well as to by-pass energy at the desired frequency which may exist there, the antenna unit consisting of the coils l9 and 20, together with the coil H, is still able effectively to cancel out the interference coming in through the antenna without any appreciable loss of signal strength.

It will be apparent in this connection that by by-passing radio frequency arising in the power line before it can be passed to the coils I 9 and 29, these coils will not act to cancel out radio frequency passing through coil I! so that a strong signal will come through While the interfering frequencies passing through coils l9 and 20, and similar interference passed by the antenna to the coil II, will cancel out.

. To permit the use of coils l9 and 20 of appropriate size, the lines 15 and ifi'incorporate condensers 28 and 29 and to avoid the possibility of radio frequency being setup in any of the coils I I,

I9 and 2!] induced, for instance, from the power line, the lower part of the lines l5 and' H5, in-

cluding condensers 2B and'29,=coils ll, 19 and 2B, are shielded by a suitable shield 35!, such as a metal shield, which is also grounded. For instance, the lead 3i may be connected to the shield and the shield in turn connected with ground ll. By employing only the antenna elimination unit consisting of the coils It and zllinductively coup-ledto the antenna coil II, all as described above, I have achieved a high degree of interference elimination. By employing these inductively coupled coils in combination with the power line interference eliminating unit, I have obtained a very marked improvement, with interference elimination substantially as high as per cent., or in other words, a substantially complete interference elimination.

What I claim as my invention is:

1. Interference eliminating means for radio receiving sets comprising a plurality of grounded inductance coils adapted to be connected in parallel circuit with a power line from which the radio receiving apparatus may receive its power, a condenser associated with each of said coils in said circuit, an inductance coil adapted to be connected in series with the antenna of the receiving set and inductively coupled with the inductance coils connected with the power line, said latter inductance coils being variable in respect to the inductance coil connected with the antenna, to produce aroundthe antenna coil a field caused by current at the interfering frequency in the power line coils, which will substantially cancel the field produced by the antenna coil as a result of current therein at the same frequency.

2. Interference eliminating means for radio receiving hookups comprising a circuit adapted to be connected in parallel with a power line from which the radio receiving apparatus may receive its power, said circuit including means for filtering out interfering audio frequency and radio frequency set up in the power line, a second circuit adapted to be connected in parallel with said power line including a plurality of grounded inductance coils having condensers in circuit therewith, an inductancecoil adapted to be connected in series withthe antenna ofthe receiving set and inductively coupled with the inductance coils connected to the power line, said latter inductance coils being variable in respect to the inductancecoil connected-with the antenna, to produce around the antenna coil a field caused bycur-rent atthe interfering frequency in the power line coils,which will substantially cancel the fieldproduced by the antenna coil as aresult of current therein at the same frequency.

3. Interference eliminating means asclaimed in claim 2 inwhich themeans for filtering out interfering audio'frequency and radio frequency from the power line includes an inductance, a condenser, a resistance and a ground and means is provided for selectively connecting some of these elements and all of these elements as required in the circuit.

FLOYD E. BOLE. 

